1. Field of the Invention
This invention relates to gas stream monitoring apparatus and particularly to such apparatus for use with gas-cooled dynamoelectric machines.
2. Description of the Prior Art
Large dynamoelectric machines occasionally fail due to thermal degradation of various materials, particularly organic insulation. Since an early detection of the insulation failure is essential to the prevention of a large scale burnout of the machine, monitoring devices are desirably used which monitor the gas streams that flow through dynamoelectric machines. Presently, most monitors work by detecting particulates in the gas stream, which are formed when insulation is being thermally degraded. When a monitor detects degradation products and generates a signal, the flow of the detectable particulates to the monitor is terminated to determine whether the signal is genuine or is due to a malfunction in the monitor. If the signal then terminates, it is assumed to be genuine and the dynamoelectric machine can be shut down for repair.
In U.S. Pat. No. 3,972,225 issued Aug. 3, 1976 it was disclosed that if the gas stream is sampled when the monitor indicates that a failure is occurring, the products collected can be analyzed to determine which material in the machine was failing. Since the location of the various materials is known, the search for the failure is considerably shortened.
It was also disclosed that the sampling can be done automatically, so that when the monitor produces a signal it can be checked for authenticity and a sample taken without human interference. In addition, it was disclosed that a particular sampling device, which separates the products of the gas streams into particles 10 microns or greater, particulates less than 10 microns, and gases is particularly useful in facilitating the analysis.
Data has been collected which shows that the pressure drop across the dynamoelectric machine's monitor used in the field is very low. The pressure drop across the vapor collector component of the disclosed vapor trap is about 9 psi at a hydrogen flow rate of 3.5 liters per minute. Because such a high head pressure is required to maintain gas flow through the vapor trap, there is an adverse effect on the particulate trap in that the particulate density is lower under the high head pressure.
In U.S. Pat. No. 3,972,225 the vapor collection trap is a column of adsorbing material such as activated charcoal, silica gel, alumina, etc., (but a modified ethylvinyl benzene-divinylbenzene copolymer sold by Waters Company under the trade name "PORAPAK R" is used). This column of adsorbing material is approximately 1/4" in diameter by about 11/2" long.